Intelligent Microgrids

Center for Electromechanic

Live field validation of an islanded microgrid based on renewables and electric vehicles

This paper presents a live field experience of creating an isolated microgrid for the Expoelectric fair during 2018 and 2019. The islanded microgrid comprises a Master Inverter with grid-forming capabilities and fault management. The Master Inverter and stationary batteries, and EVs with V2G capabilities provide storage. A PV generation system supplies the microgrid. The loads are the fair booths, mainly lighting and chargers for personal mobility vehicles. All the equipment used in the experimental microgrid is from different manufacturers. The operation and control of the islanded microgrid are based on the VDE-AR-N-4105 standard. The paper also presents the operation of the Master Inverter during faults. The live field experience shows that the proposed operation method is valid for operating different converters from different manufacturers without needing any communication layer between them. The experimental results also show that faults can be handled correctly by the Master Inverter to operate the entire microgrid safely. In conclusion, islanded microgrids based on power electronics are feasible to replace diesel generators in faires, conventions or temporary events.Peer ReviewedPostprint (published version

Adaptive Reference Trajectory for Power Quality Enhancement in Three-Phase Four-Wire Standalone Power Supply Systems with Nonlinear and Unbalanced Loads

International audienc

A Hybrid State/Event Driven Communication-based Control for DC Microgrids

The U.S. electric power industry is undergoing unprecedented changes triggered by the growing electricity demand, and the national efforts to reduce greenhouse gas emissions. Moreover, there is a call for increased power grid resiliency, survivability and self-healing capabilities. As a result of these challenges, the smart grid concept emerged. One of the main pillars of the smart grid is microgrids. In this thesis, the technical merits of clustering multiple microgrids during blackouts on the overall stability and supply availability have been investigated. We propose to use the existing underground distribution grid infrastructure, if applicable, during blackouts to form microgrid clusters. The required control hierarchy to manage microgrid clusters, and communicate with the Distribution Network Operator (DNO) has been discussed. A case study based on IEEE standard distribution feeders, and two microgrid models, has been presented. Results show that clustering microgrids help improve their performance and that the microgrid total rotating mass inertia has a direct impact on the overall stability of a microgrid cluster. The design and control of individual microgrids have been given genuine attention in this thesis since they represent the main resiliency building block in the proposed clustering approach. Therefore, a considerable portion of this thesis is dedicated to present studies and results of designing, simulating, building and testing a direct current (DC) microgrid. The impact of various operational scenarios on DC microgrid performance has been thoroughly discussed. Specifically, this thesis presents the design and implementation of the City College of New York (CCNY) DC microgrid laboratory testbed. The experimental results verify the applicability and flexibility of the developed microgrid testbed. An autonomous communication-based centralized control for DC microgrids has been developed and implemented. The proposed controller enables a smooth transition between various operating modes. Finite state machine (FSM) has been used to mathematically describe the various operating modes (states), and the events that may lead to mode changes (transitions). Therefore, the developed centralized controller aims at optimizing the performance of MG during all possible operational scenarios, while maintaining its reliability and stability. Results of selected drastic cases have been presented, which verified the validity and applicability of the proposed controller. Since the proposed microgrid controller is communication-based, this thesis investigates the effect of wireless communication technologies latency on the performance of DC microgrids during islanding. Mathematical models have been developed to describe the microgrid behavior during communication latency. Results verify the accuracy of the developed models and show that the impact may be severe depending on the design, and the operational conditions of the microgrid just before the latency occurs. We propose to use the existing underground distribution grid infrastructure, if applicable, during blackouts to form microgrid clusters. The required control hierarchy to manage microgrid clusters, and communicate with the Distribution Network Operator (DNO) has been discussed. A case study based on IEEE standard distribution feeders, and two microgrid models, has been presented. Results show that clustering microgrids help improve their performance and that the microgrid total rotating mass inertia has a direct impact on the overall stability of a microgrid cluster. The design and control of individual microgrids have been given genuine attention in this thesis since they represent the main resiliency building block in the proposed clustering approach. Therefore, a considerable portion of this thesis is dedicated to present studies and results of designing, simulating, building and testing a direct current (DC) microgrid. The impact of various operational scenarios on DC microgrid performance has been thoroughly discussed. Specifically, this thesis presents the design and implementation of the City College of New York (CCNY) DC microgrid laboratory testbed. The experimental results verify the applicability and flexibility of the developed microgrid testbed. An autonomous communication-based centralized control for DC microgrids has been developed and implemented. The proposed controller enables a smooth transition between various operating modes. Finite state machine (FSM) has been used to mathematically describe the various operating modes (states), and the events that may lead to mode changes (transitions). Therefore, the developed centralized controller aims at optimizing the performance of MG during all possible operational scenarios, while maintaining its reliability and stability. Results of selected drastic cases have been presented, which verified the validity and applicability of the proposed controller. Since the proposed microgrid controller is communication-based, this thesis investigates the effect of wireless communication technologies latency on the performance of DC microgrids during islanding. Mathematical models have been developed to describe the microgrid behavior during communication latency. Results verify the accuracy of the developed models and show that the impact may be severe depending on the design, and the operational conditions of the microgrid just before the latency occurs

Optimization Techniques for Modern Power Systems Planning, Operation and Control

Recent developments in computing, communication and improvements in optimization techniques have piqued interest in improving the current operational practices and in addressing the challenges of future power grids. This dissertation leverages these new developments for improved quasi-static analysis of power systems for applications in power system planning, operation and control. The premise of much of the work presented in this dissertation centers around development of better mathematical modeling for optimization problems which are then used to solve current and future challenges of power grid. To this end, the models developed in this research work contributes to the area of renewable integration, demand response, power grid resilience and constrained contiguous and non-contiguous partitioning of power networks. The emphasis of this dissertation is on finding solutions to system operator level problems in real-time. For instance, multi-period mixed integer linear programming problem for applications in demand response schemes involving more than million variables are solved to optimality in less than 20 seconds of computation time through tighter formulation. A balanced, constrained, contiguous partitioning scheme capable of partitioning 20,000 bus power system in under one minute is developed for use in time sensitive application area such as controlled islanding

Communication Based Control for DC Microgrids

Centralized communication-based control is one of the main methods that can be implemented to achieve autonomous advanced energy management capabilities in DC microgrids. However, its major limitation is the fact that communication bandwidth and computation resources are limited in practical applications. This can be often improved by avoiding redundant communications and complex computations. In this paper, an autonomous communication-based hybrid state/event driven control scheme is proposed. This control scheme is hierarchical and heuristic, such that on the primary control level, it encompasses state-driven local controllers, and on the secondary control level, an event-driven MG centralized controller (MGCC) is used. This heuristic hybrid control system aims at reducing the communication load and complexity, processor computations, and consequently system cost while maintaining reliable autonomous operation during all possible scenarios. A mathematical model for the proposed control scheme using Finite State Machines (FSM) has been developed and used to cover all the possible modes/sub-modes of operation, and assure seamless transitions among them during various events. Results of some case studies involving severe operational scenarios were presented and discussed. Results verify the validity and effectiveness of the proposed communication-based control scheme

Protection of Microgrids: A Scalable and Topology Agnostic Scheme With Self-Healing Dynamic Reconfiguration

Momentum towards realizing the smart grid will continue to result in high penetration of renewable fed Distributed Energy Resources (DERs) in the Electric Power System (EPS). These DERs will most likely be Inverter Based Resources(IBRs) and will be an integral part of the distribution system in the near future. The drive towards resiliency with these IBRs will enable a modular topology where several microgrids are tied together, operating synchronously to form the future EPS at the distribution level. Since the microgrids can evolve from existing distribution feeders, they will be unbalanced in load, phases, and feeder impedances. A typical control strategy of a conventional inverter that follows the grid voltage and frequency while injecting positive-sequence current can lead to undesirable performance for the unbalanced systems, especially in the islanded mode of operation. So, the dissertation will first focus on the control aspect of IBRs in an unbalanced system. Acceptable operating conditions with stability against disturbances and faults are the primary focus. For the proper functioning of these microgrids, there is a need for grid-forming inverters that can enable acceptable performance and coexist with conventional grid-following inverters that supply only positive-sequence currents. In addition to the control objectives, limiting inverter output during faulted or overload conditions with a current limiter is essential. These control objectives can be implemented in both the synchronous reference frame ($dq$ coordinates) and the natural reference frame ($abc$ coordinates). Hence a comparison study is performed to understand the merit of each implementation related to this specific topology. As 100\% IBR-based microgrid becomes an integral part of the distribution system, the issues and challenges arising from its implementation should be addressed for successful operation. Designing reliable protection is one of the significant challenges for microgrids. Most microgrid protection schemes found in published literature suffer from a lack of generality. They work well for the assumed topology, including the type and placement of sources. Other generic protection schemes tend to be too complicated, expensive, or both. To overcome these drawbacks, a topology-agnostic, scalable, and cost-aware protection based on fundamental principles is developed that works in the presence of high penetration of inverter-based resources (IBRs). The protection system includes primary and backup. It also implements stable automatic reconfiguration of the healthy sections of the system after clearance of fault, thus increasing resilience by self-healing. The scheme is validated in PSCAD for primary and backup protection and reconfiguration on the IEEE 123-node feeder in grid-connected and islanded modes with 15 IBRs connected to the system. As the designed protection scheme requires communication between protective devices and the microgrid controller, the method must be validated in real-time with cyber-physical co-simulation for a successful demonstration. In this regard, a Hardware-In-the-Loop (HIL) platform between a simulated power system model using RTDS and physical protective devices is built. In the HIL platform, the primary protection of the scheme is programmed in SEL 421-7 relay, and backup protection is programmed in MATLAB on a generic computer acting as a microgrid controller. The IEC 61850 models are used to communicate between the SEL-421-7 relay and RTDS, whereas TCP/IP communication connects the microgrid controller to RTDS. The focus of the work is to demonstrate the co-simulation platform with communication links established using both protocols and validate the proposed scheme in real-time on the IEEE 123 node distribution feeder. The IEC 61850 and TCP/IP communications configuration are discussed as the interface requires proper hardware and software setup. The real-time performance indicates the Hardware In the Loop (HIL) framework as a competent testing environment for the developed protection scheme for microgrids. In summary, a scalable and topology agnostic protection scheme with self-healing dynamic reconfiguration is developed for microgrids. Clear guidelines for implementation of the proposed scheme on any microgrid topology are also described